Estimation of Surface Runoff In Northeastern Missan Governorate by Using (Nrcs-Cn) Technique And Gis

Abstract

In this study, an attempted was made to estimate average of annual total surface runoff in the
 northeastern Missan Governorate, south of Iraq by using Natural Resources Conservation Services
 Curve Number (NRCS – CN) empirical technique in GIS platform. Thematic layers of soil
 hydrological groups and LULC were created using ArcGIS 9.3 software. Intersection of these two
 thematic layers generated a map with new polygons representing the merged hydrological soil group
 and LULC. The appropriated CN values adapted from different sources and technical release of
 United State of Department of Agriculture (USDA) were assigned manually for each new merged
 polygon. The curve numbers for different antecedent moisture content (AMC) were calculated as 38,
 59, 77 for dry, normal, and wet soil conditions. The associated maximum potential retention for each
 AMC were calculated as 75,87, 176.51, and 414.42 for dry, normal, and wet soil moisture conditions.
 Application of the method showed that the average annual runoff depth is 0.36 mm. This figure was
 multiplied by the area of the study area (1856) km2 to get the total average of runoff volume 7424000m3 
 which represents 0.0003 from the total annual average of rainfall. The applied method is robust
 and easy to implement and could be used to roughly estimate the surface runoff with minimal data.